Methods of fabricating composite structures include the fiber placement or automated collation process. In such a process, one or more ribbons of composite material or tows may be laid down on a substrate which may be a tool, mandrel or one or more underlying and compacted layers of composite material. Conventional fiber placement processes may utilize a heat source to assist in compaction of the plies of composite material at a localized nip point. The ribbon or tow of composite material and the underlying substrate may be heated at the nip point to increase the tack of the resin of the plies while being subjected to compressive forces to ensure adhesion to the substrate. To complete the part, additional strips of composite material may be applied in a side-by-side manner to form layers and may be subjected to localized heat and pressure during the consolidation process.
A complex and detailed inspection guideline may be necessary for the inspection of composite structures that are fabricated using the fiber and tape placement processes. The guideline may establish acceptance criteria for discrete inconsistencies such as tow gaps, tow overlaps, twists, dropped tows and foreign objects. In-process vision technology may be capable of detecting and making accept/reject decisions on these inconsistencies during the manufacturing process. The guideline may also establish a requirement for maximum allowable cumulative, or total, tow gap width within any 12-inch area perpendicular to the direction of material placement or lay-down.
The existing solution to meeting the requirements of the inspection guidelines may include manual visual inspection by the human eye. An operator may select at random a number of regions of the correct size according to the inspection guideline. The operator may then apply a manual template that will define the area in which the inspection is to be made. The operator may utilize a means, of determining and documenting the location, of the region with respect to the entire surface area of the ply. Within each area, the operator may be required to visually identify tow gaps and measure each one manually using a tool such as a six-inch scale or a dial caliper. The widths of all identified gaps may be documented, the sum of the gap widths may be calculated and the sum for the specific area may be determined. The approach may be carried out on each ply of each part which is manufactured.
The existing solution to meeting the requirements of the inspection guidelines may require extensive cycle time and touch labor and may carry a high risk of inaccurate measurement. This approach may be viable for small parts but unmanageable for large surface areas. The approach may also be labor-intensive and prone to a high probability of error in measurement. Reduction of fatigue and risk of error may require multiple inspectors which may increase the touch labor required to complete the inspection.
The disclosure is generally directed to a system for determining cumulative tow gap width. An illustrative embodiment of the system includes an in-process vision system having at least one camera adapted to record images of a composite material and a data analysis computer communicating with and adapted to receive image data from the in-process vision system. The data analysis computer may be adapted to calculate a cumulative gap width of tow gaps in the composite material. A user interface may communicate with and be adapted to receive data analysis results from the data analysis computer.
The disclosure is further generally directed to a method for determining cumulative tow gap width of tow gaps in a composite structure. An illustrative embodiment of the method includes providing a composite material, recording periodic images of the composite material, analyzing the images of the composite material for presence of rejectable indications in the composite material and formulating a pass/fail status of the composite material based on the rejectable indications.